1. Field of the Invention
The present invention relates to a process for preparing an absorbent foam. The process generally comprises forming a solution of a soluble polymer in a solvent, freezing the solution at a relatively slow cooling rate to a temperature below the freezing point of the solvent, removing the solvent from the frozen solution, and recovering the polymer to form a water-swellable, water-insoluble polymeric foam. The process has been found to enable one to prepare an absorbent foam that exhibits desirable softness and flexibility properties yet is highly absorbent. Such an absorbent foam may be used in a disposable absorbent product intended for the absorption of fluids such as body fluids.
2. Description of the Related Art
Disposable absorbent products currently find widespread use in many applications. For example, in the infant and child care areas, diapers and training pants have generally replaced reusable cloth absorbent articles. Other typical disposable absorbent products include feminine care products such as sanitary napkins or tampons, adult incontinence products, and health care products such as surgical drapes or wound dressings. A typical disposable absorbent product generally comprises a composite structure including a topsheet, a backsheet, and an absorbent structure between the topsheet and backsheet. These products usually include some type of fastening system for fitting the product onto the wearer.
The use of water-swellable, generally water-insoluble absorbent materials, commonly known as superabsorbents, in disposable absorbent personal care products is known. Such absorbent materials are generally employed in absorbent products in order to increase the absorbent capacity of such products while reducing their overall bulk. Such absorbent materials are generally present in absorbent products in the form of small particles in a fibrous matrix, such as a matrix of wood pulp fluff. A matrix of wood pulp fluff generally has an absorbent capacity of about 6 grams of liquid per gram of fluff. The superabsorbent materials generally have an absorbent capacity of at least about 10, preferably of about 20, and often of up to 100 times their weight in water. Clearly, incorporation of such absorbent materials in disposable absorbent products can reduce the overall bulk while increasing the absorbent capacity of such products.
As an alternative to using a fibrous matrix containing superabsorbent materials, absorbent foams are also known. One form of an absorbent foam is wherein a foam material, such as polyurethane, is prepared to include a particulate superabsorbent material within the structure of the polyurethane foam. Alternatively, a particulate superabsorbent material is located between at least two layers of a polyurethane foam material to form a layered composite structure. While such foam structures may be useful absorbent materials in specific applications, they have not been shown to be optimal for use in disposable absorbent products because their absorptive properties tend to be limited. In particular, the foam material is such structures, such as polyurethane, generally does not have a sufficient absorptive ability to retain liquids. Therefore, although the particulate superabsorbent material in the foam structure may be able to retain a liquid, the overall capacity of the foam structure to absorb and retain a liquid is limited. Furthermore, the overall absorptive properties of the foam structure tend to be limited due to the relatively low surface area to mass ratio of the particulate superabsorbent material portion relative to the foam portion of the structure.
Absorbent foams are also known that are prepared comprising essentially all superabsorbent material. Typically, a blowing agent is used to form a foamed, water-swellable, polymeric liquid absorbent material. However, certain absorbent foams prepared using specific blowing agents have been found to have limited use for liquid absorption or liquid distribution. This is typically due to physical characteristics of the foam structure, which may include discontinuous channels, a too large average cell size, unacceptably wide cell size distribution, and/or capillary diameters that vary widely and randomly, that tend to result in undesirable absorptive rates and capacities and undesirable liquid distribution properties. In addition, known absorbent foams that are prepared comprising essentially all superabsorbent material have typically been found to have undesirable non-absorptive physical characteristics such as a lack of softness or being too brittle. Furthermore, many of the known foams are hydrophobic in nature and need treatment with a wetting agent or other suitable treatment steps to obtain a hydrophilic nature. Such undesirable non-absorptive physical characteristics of an absorbent foam tends to limit the usefulness of the absorbent foam in disposable absorbent products since such disposable absorbent products generally need to be sufficiently flexible to withstand the rigors of use by a consumer and also be sufficiently soft to be acceptably comfortable during use.
Thus, there is a continuing need for improvement of absorbent foams. In particular, there is a need for an absorbent foam which exhibits a relatively high absorptive liquid capacity yet which exhibits desirable softness and flexibility properties. In addition, there is a need for a process for preparing such an absorbent foam that is simple, safe, and cost-effective.
It is therefore an object of the present invention to provide a process for preparing an absorbent foam that is simple, safe, and cost-effective.
It is also an object of the present invention to provide a disposable absorbent product which includes an absorbent foam that exhibits a relatively high absorptive liquid capacity yet which exhibits desirable physical characteristics such as softness and flexibility properties.